The invention relates to a method for electrolytic etching of silicon carbide SiC, which is arranged in series with an electrolyte and a metallic counter-electrode in a current circuit with an adjustable direct voltage.
SiC is suitable as a high-temperature and high-power component due to its physical properties. Due to the difficulties in the production of suitable monocrystals, very few crystal wafers are available, and therefore the methods required for subsequent processing are not developed to a great extent.
For subsequent processing, it is also important to have the smoothest possible substrate surface. Since a disturbed surface, a so-called damage layer, is usually left in the range of several micrometers after conventional mechanical polishing, methods for polish-etching were developed for semiconductors (for example, for silicon, germanium as well as gallium arsenide or indium phosphide) which remove the damage layer and result in an even surface. With this polish-etching, there is a reduction in thickness of the material, which is generally in wafer form, while maintaining the even surface formation, in that the peak atoms, which possess a lower bonding energy in the crystal lattice, are removed first. In most cases, chemical etchants or chemical-mechanical polishing methods are used. However, electrolytic etching methods are also known, which mostly work with acid electrolytes and, in rare cases, with alkaline ones. Polish-etching of the surface, for example of germanium, is carried out with a current density of up to 50 mA/cm.sup.2, with caustic potash solution as the electrolyte, the concentration of which amounts to approximately 0.01% (Bogenschutz "Atzpraxis fur Halbleiter" ["Etching Practice for Semiconductors"], pages 138 to 142, Karl Hanser Verlag, Munich, 1967).
A known aqueous etching method for silicon carbide SiC at room temperature is electrolytic etching with hydrofluoric acid as the electrolyte. Etching takes place at a current density of up to approximately 0.5 A/cm.sup.2 and a concentration of the electrolyte of up to approximately 2%. This results in textured etching, with which a stronger attack of the etchant on the surface takes place in the areas with lattice defects, for example; in these areas, depressions are therefore obtained (Mat. Res. Bull., Vol. 4 (1969), pages 199 to 210, Pergamon, Inc., USA).